\begin{tikzpicture}
\node (a) at (0,0){(1)$\rm{e 1=a^{*} b^{+}}$};
\node (a1) at ([xshift=-3em,yshift=0em]a.west){【例】};
\node (b) at ([xshift=4em,yshift=-2em]a.south) {$\rm{L(e 1)=\left\{a^{m} b^{n} \mid m \geqslant 0, n \geqslant 1\right\}}$;};
\node (c) at ([xshift=3.5em,yshift=-2em]b.south) {$\rm{=\{b, a b, b b, a a a b, a a b, a b b, a a b b, \ldots\}}$};
\node (d) at ([xshift=-6em,yshift=-2em]c.south){$\rm{(2)\ e2=(a b)^{+}}$};
\node (e) at ([xshift=2em,yshift=-2em]d.south){$\rm{L(e 2)=\left\{(a b)^{n} \mid n \geqslant 1\right\},}$};
\node (f) at ([xshift=5em,yshift=-2em]e.south){$\rm{=\{a b, a b a b, a b a b a b, a b a b a b a b, \ldots\}}$};
\node (g) at ([xshift=-6em,yshift=-2em]f.south){$\rm{(3) e 3=a b^{*} c \mid b^{*}}$};
\node (h) at ([xshift=-1em,yshift=-5em]f.south){$\rm{L(e 3)=\left\{a b^{n} c, \quad b^{n} \mid n \geqslant 0\right\}}$};
\node (i) at ([xshift=6em,yshift=-2em]h.south){$\rm{=\{a c, a b c, a b b c, a b b b c, \ldots ; \varepsilon, b, b b, b b b, \ldots\}}$};
\node(c1)[draw,fill=purple!30,rounded corners,align=center] at ([xshift=5em,yshift=3em]c.east) {展开:};
 \draw[->,red] ([xshift=0em,yshift=0em]c1.south) --([xshift=0em,yshift=0em]c.east);
\draw[->,red] ([xshift=0em,yshift=0em]c1.south) --([xshift=0em,yshift=0em]f.east);
\draw[->,red] ([xshift=0em,yshift=0em]c1.south) --([xshift=0em,yshift=0em]i.east);
\begin{pgfonlayer}{background}
\node [fill=red!20,fit=(b)] {};
\end{pgfonlayer}
\begin{pgfonlayer}{background}
\node [fill=red!20,fit=(e)] {};
\end{pgfonlayer}
\begin{pgfonlayer}{background}
\node [fill=red!20,fit=(h)] {};
\end{pgfonlayer}
\begin{pgfonlayer}{background}
\node [fill=yellow!20,fit=(c)] {};
\end{pgfonlayer}
\begin{pgfonlayer}{background}
\node [fill=yellow!20,fit=(f)] {};
\end{pgfonlayer}
\begin{pgfonlayer}{background}
\node [fill=yellow!20,fit=(i)] {};
\end{pgfonlayer}
\end{tikzpicture}